Optical compensatory sheet comprising polymer film

ABSTRACT

A polymer film is used as an optical compensatory sheet or a support thereof. The polymer film contains a rod-like compound. The rod-like compound in the form of a solution gives an ultraviolet absorption spectrum. In the spectrum, the wavelength of λmax at the maximum absorption peak is shorter than 250 nm. The spectrum of the rod-like compound is measured when the rod-like compound is in the form of solution. The polymer film has an Rth retardation value of Rth450 measured at the wavelength of 450 nm in the range of 30 to 160 nm. The polymer film also has an Rth retardation value of Rth590 measured at the wavelength of 590 nm in the range of 50 to 200 nm. The values of the Rth450 and Rth590 satisfy the condition of Rth590-Rth450≧2 nm.

FIELD OF INVENTION

The present invention relates to an image-displaying device,particularly an optical compensatory sheet and a polarizing plate thatcan improve the recognizability and the viewing angle of liquid crystaldisplay. Also, the invention relates to an image-displaying deviceimproved in both recognizability and viewing angle.

BACKGROUND OF INVENTION

A liquid crystal display generally comprises a polarizing plate and aliquid crystal cell.

Since the liquid crystal display has a narrow viewing angle, it has beenproposed to use an optical compensatory sheet for enlarging the viewingangle (for example, in Japanese Patent provisional Publication Nos.4(1992)-229828, 4(1992)-258923, 6(1994)-75116, 6(1994)-174920 and6(1994)-222213).

A TFT liquid crystal display of TN mode (which is nowadays mainly used)is equipped with an optical compensatory sheet comprising a support anda thereon-provided optically anisotropic layer formed from liquidcrystal compound. The optical compensatory sheet is placed between thepolarizing plate and the liquid crystal cell, to optically compensatethe viewing angle dependence of; the cell so that the quality ofdisplayed image may be improved. That compensatory sheet is describedin, for example, 8(1996)-50206.

Also, a wide-viewing angle polarizing plate comprising a birefringenciallayer as a protective film is proposed to prevent the plate itself fromleaking light when obliquely seen. That plate is described in, forexample, 10(1998)-48420.

SUMMARY OF INVENTION

Recently, liquid crystal displays have been used in various fields. Asthe displays become used for many purposes, their displaying screens aregetting larger and larger. The display with a large screen of 17-inchesor more often suffers troubles that were already solved by prior arts ina conventional display with a small screen. The troubles are, forexample, fluctuations of displayed image qualities (contrast, color andtone), and particularly it is getting more and more wanted to avoid thefluctuation of color.

The inventor also found that, in the case where a polarizing plateequipped with the aforementioned optical compensatory sheet as theprotective film is attached on a large display panel of 17-inches ormore, the light leakage caused by thermal distortion is not fullyprevented. It is, therefore, necessary for the optical compensatorysheet to have not only the function of optically compensating the liquidcrystal cell but also excellent durability against change of theenvironmental conditions.

An object of the present invention is to effectively compensate a liquidcrystal display even if it has a large displaying screen.

Another object of the invention is to give a polarizing plate an opticalcompensating function without increasing elements of the plate.

A further object of the invention is to provide a liquid crystal displayhaving a large displaying screen and giving an image with highqualities.

A furthermore object of the invention to optically compensate a liquidcrystal cell by means of an optical compensatory sheet excellent indurability.

A still furthermore object of the invention to provide a liquid crystaldisplay prevented from leaking light by means of an optical compensatorysheet placed on one side of the polarizing plate, and thereby to improvequalities of images given by the display.

The present invention provides optical compensatory sheets (1) to (9), apolarizing plate (10) and the image displaying devices (11) and (12).

(1) An optical compensatory sheet which consists of a polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm.

(2) An optical compensatory sheet which comprises an opticallyanisotropic layer and a polymer film, said optically anisotropic layerbeing formed from a liquid crystal compound, and said polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of.30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm.

The Rth retardation value is defined by the following formula (I):Rth={(nx+ny)/2-nz}×d   (I)in which nx is a refractive index along the show axis in the film plane;ny is a refractive index along the fast axis in the film plane; nz is arefractive index along the depth of the film; and d is thickness of thefilm in terms of nm.

(3) The optical compensatory sheet of (1) or (2), wherein the polymerfilm has an Re retardation value of Re450 measured at the wavelength of450 nm in the range of 10 to 60 nm, and an Re retardation value of Re590measured at the wavelength of 590 nm in the range of 20 to 70 nm, saidvalues of Re450 and Re590 satisfying the condition of Re590-Re450≧2 nm.

The Re retardation value is defined by the following formula (II):Re=(nx−ny)×d   (II)in which nx is a refractive index along the show axis in the film plane,ny is a refractive index along the fast axis in the film plane, and d isthickness of the film in terms of nm.

(4) The optical compensatory sheet of (1) or (2), wherein the polymerfilm is made of cellulose ester.

(5) The optical compensatory sheet of (1) or (2), wherein the polymerfilm is a film stretched with a stretching ratio of 3 to 100%.

(6) The optical compensatory sheet of (1) or (2), wherein the rod-likecompound has a linear molecular structure.

(7) The optical compensatory sheet of (1) or (2), wherein the rod-likecompound is liquid crystal.

(8) The optical compensatory sheet of (1) or (2), wherein the rod-likecompound is represented by the formula (III):Ar¹-L¹-Ar²   (III)in which each of Ar¹ and Ar² independently is an aromatic group; and L¹is a divalent linking group selected from the group consisting of analkylene group, an alkenylene group, an alkynylene group, a divalentsaturated heterocyclic group, —O—, —CO— and a combination thereof.

(9) The optical compensatory sheet of (7), wherein the rod-like compoundis represented by the formula (IV):Ar¹-L²-X-L³-Ar²   (IV)in which each of Ar¹ and Ar² independently is an aromatic group; each ofL² and L³ independently is a divalent linking group selected from thegroup consisting of an alkylene group, —O—, —CO— and a combinationthereof; and X is 1,4-cyclohexylene, vinylene or ethynylene.

(10) A polarizing plate comprising a pair of transparent protectivefilms and a polarizing membrane provided between the transparentprotective films, wherein at least one of the protective films is anoptical compensatory sheet of (1) or (2), and wherein the opticalcompensatory sheet and the polarizing membrane are so placed that thetransmission axis of the membrane is parallel or perpendicular to theslow axis of the polymer film.

(11) An image display device having an optical compensatory sheet (1) or(2).

(12) An image display device having a polarizing plate (10).

A liquid crystal display generally comprises a pair of polarizing platesplaced in cross-Nicol arrangement (so that the transmission axes of theplates may be perpendicularly crossed). When the plates placed incross-Nicol arrangement are obliquely seen, the appearing angle betweenthe axes is not seen to be 90° and consequently the plates leak light.Although a convention optical compensatory sheet (for example, describedin Japanese Patent Provisional Publication No. 10(1998)-48420) canprevent the light leakage, it undesirably colors the displayed image.The inventor has found this undesirable coloring is caused by thewavelength dispersion of the compensatory sheet. Accordingly, forpreventing the undesirable coloring, it is necessary for thecompensatory sheet to increase retardation in proportion to increase ofthe wavelength.

It is already known to use a retardation-increasing agent for adjustingthe retardation, but conventional retardation-increasing agents oftengive retardation deviated from the aimed values particularly in ashort-wavelength range.

The inventor has studied and finally found that, if a rod-like compoundgiving the maximum absorption peak at a wavelength (λmax) shorter than250 nm in its ultraviolet absorption spectrum when the compound is inthe form of solution is used as a retardation-increasing agent, theretardation can be adequately adjusted in a wide wavelength regionincluding a short-wavelength range.

Consequently, the invention reduces the color fluctuation depending uponthe viewing angle. In particular, the invention effectively improves thequalities of image given by a large liquid crystal display.

DETAILED DESCRIPTION OF INVENTION

(Retardation of Polymer Film)

The polymer film has an Rth retardation value measured at the wavelengthof 450 nm (Rth450) in the range of 30 to 160 nm, and an Rth retardationvalue measured at the wavelength of 590 nm (Rth590) in the range of 50to 200 nm. The Rth450 and the Rth590 satisfy the condition ofRth590-Rth450≧2 nm, preferably Rth590-Rth450≧5 nm, and more preferablyRth590-Rth450≧10 nm.

Preferably, the polymer film has a Rth retardation value measured at thewavelength of 450 nm (Rth450) in the ranges of 45 to 150 nm, another Rthretardation value measured at the wavelength of 550 nm (Rth550) in theranges of 55 to 180 nm, and still another Rth retardation value measuredat the wavelength of 590 nm (Rth590) in the ranges of 70 to 185 nm. Theypreferably satisfy the condition of Rth590-Rth450≧2 nm, more preferablysatisfy the condition of Rth590-Rth550≧2 nm, most preferably satisfy thecondition of Rth590-Rth550≧2 nm. It is also preferred to satisfy thecondition of Rth550-Rth450≧10 nm.

The Rth retardation value is defined by the following formula (I):Rth={(nx+ny)/2-nz}×d   (I)in which nx is a refractive index along the show axis in the film plane,ny is a refractive index along the fast axis in the film plane, nz is arefractive index along the depth of the film, and d is thickness of thefilm in terms of nm.

Further, the polymer film has a Re retardation value measured at thewavelength of 450 nm (Re450) in the ranges of 10 to 60 nm, and anotherRe retardation value measured at the wavelength of 590 nm (Rth590) inthe ranges of 20 to 70 nm. The Re450 and the Re590 satisfy the conditionof Re590-Re450≧0.2 nm, preferably Re590-Re450≧1 nm, and more preferablyRe590-Re450≧2 nm.

Preferably, the polymer film has a Re retardation value measured at thewavelength of 450 nm (Re450) in the ranges of 15 to 50 nm, another Reretardation value measured at the wavelength of 550 nm (Re550) in theranges of 20 to 60 nm, and still another Re retardation value measuredat the wavelength of 590 nm (Re590) in the ranges of 25 to 70 nm. Theypreferably satisfy the condition of Re590-Re550≧0.2 nm, more preferablysatisfy the condition of Re590-Re550≧0.5 nm, most preferably satisfy thecondition of Re590-Re550≧1 nm. It is also preferred to satisfy thecondition of Re550-Re450≧2 nm.

The Re retardation value is defined by the following formula (II):Re=(nx−ny)×d   (II)in which nx is a refractive index along the show axis in the film plane,ny is a refractive index along the fast axis in the film plane, and d isthickness of the film in terms of nm.(Polymer)

The polymer film is preferably made of a polymer having alight-transmittance of 80% or more. Examples of the polymer includecellulose esters (e.g., cellulose acetate), norbornene-based polymers,polyacrylic esters, polymethacrylic esters (e.g., polymethylmethacrylate), polycarbonates and polysulfones. Commercially availablepolymers such as Artone and Zeonex (norbornene-based polymers) may beused.

Cellulose esters are preferred, and cellulose esters of lower fattyacids are more preferred. Here, the term “lower fatty acids” means fattyacids having 6 or less carbon atoms. The number of carbon atoms ispreferably 2 (cellulose acetate), 3 (cellulose propionate) or 4(cellulose butyrate). Cellulose esters of mixed fatty acids such ascellulose acetatepropionate and cellulose acetatebutyrate are alsousable. Cellulose acetate is particularly preferred.

The acetic acid content of cellulose acetate is preferably in the rangeof 55.0 to 62.5%, more preferably in the range of 57.0 to 62.0%. Theterm “acetic acid content” means the amount of combined acetic acid perone unit weight of cellulose. The acetic acid content can be determinedaccording to ASTM: D-817-91 (tests of cellulose acetate).

The cellulose ester has a viscosity average polymerization degree (DP)of preferably 250 or more, more preferably 290 or more. Further, it isalso preferred for the cellulose ester used in the invention to have anarrow molecular weight distribution of Mw/Mn (Mw and Mn are weight andnumber average molecular weights, respectively), which is determined bygel permeation chromatography. The value of Mw/Mn is preferably in therange of 1.0 to 1.7, more preferably in the range of 1.3 to 1.65, mostpreferably in the range of 1.4 to 1.6.

Generally in a cellulose ester, hydroxyl groups at 2-, 3- and 6-positionof cellulose unit are not equally substituted (namely, the substitutiondegree at each position is not equal to one third of the totalsubstitution degree), and the substitution degree at 6-position is aptto be relatively small. In the cellulose ester used in the invention,the substitution degree at 6-position is preferably not smaller thanthose at 2- and 3-positions.

The hydroxyl group at 6-position is substituted in an amount ofpreferably 30% to 40%, more preferably 31% or more, most preferably 32%or more, based on the total substitution degree at 2-, 3- and6-positions. Further, the substitution degree at 6-position ispreferably 0.88 or more. The hydroxyl group at 6-position may besubstituted with acyl group other than acetyl. Examples of the otheracyl group are acyl groups having 3 or more carbon atoms (e.g.,propionyl, butyloyl, valeroyl, benzoyl, acryloyl). The substitutiondegree at each position can be measured by means of NMR.

The cellulose ester having a high substitution degree at 6-position canbe prepared according to the methods described in Japanese PatentProvisional Publication No. 11(1999)-5851.

(Retardation-Increasing Agent)

In the invention, a rod-like compound giving the maximum absorption peakat a wavelength (λmax) shorter than 250 nm in its ultraviolet absorptionspectrum when the compound is in the form of solution is used as aretardation-increasing agent.

The rod-like compound has preferably at least one aromatic ring, morepreferably at least two aromatic rings in its molecular structure, inconsideration of the retardation-increasing function.

Further, the rod-like compound preferably has a linear molecularstructure. In other wards, it is preferred for the molecule of thecompound to be thermally the most stable when it takes a linear posture.What molecular structure is thermally the most stable can be calculatedaccording to the crystal structure analysis or the molecular orbitalmethod. For example, the molecular structure giving the smallest heat offormation can be obtained by calculation according to a molecularorbital calculation program (e.g., WinMOPAC200, Fujitsu, Ltd.). The term“linear molecular structure” means that the thermally most stablemolecular structure calculated above has a bending angle of 140° or moreeven if it is bent.

The rod-like compound preferably behaves as liquid crystal. It is morepreferred to behave as liquid crystal when heated (namely, thermotropicliquid crystal). The liquid crystal phase is preferably nematic phase orsmectic phase.

The rod-like compound is preferably represented by the following formula(III):Ar¹-L¹-Ar².   (III)

In the formula (III), each of Ar¹ and Ar² is independently an aromaticgroup.

The term “an aromatic group” in the specification means an aryl(aromatic hydrocarbon) group, a substituted aryl group, an aromaticheterocyclic group or a substituted aromatic heterocyclic group.

An aryl group and a substituted aryl group are preferred to an aromaticheterocyclic group and a substituted aromatic heterocyclic group. Thearomatic heterocyclic group preferably comprises a five-membered,six-membered or seven-membered (more preferably five-membered orsix-membered) aromatic heterocyclic ring. The aromatic heterocyclic ringis generally unsaturated and has double bonds as many as possible. Thehetero atom in the heterocyclic group is preferably nitrogen, oxygen orsulfur atom, more preferably nitrogen or sulfur atom. Examples of thearomatic heterocyclic ring include furan ring, thiophene ring, pyrrolering, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring,imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring,pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring and1,3,5-triazine ring.

The aromatic ring in the aromatic group preferably is benzene ring,furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring,imidazole ring, triazole ring, pyridine ring, pyrimidine ring orpyrazine ring. Benzene ring is particularly preferred.

Examples of the substituent group of the substituted aryl or substitutedaromatic heterocyclic group include a halogen atom (F, Cl, Br, I),hydroxyl, carboxyl, cyano, amino, an alkylamino group (e.g.,methylamino, ethylamino, butylamino, dimethylamino), nitro, sulfo,carbamoyl, an alkylcarbamoyl group (e.g., N-methylcarbamoyl,N-ethylcarbamoyl, N,N-dimethylcarbamoyl), sulfamoyl, an alkylsulfamoylgroup (e.g., N-methylsulfamoyl, N-ethylsulfamoyl,N,N-dimethylsulfamoyl), ureido, an alkylureido group (e.g.,N-methylureido, N,N-dimethylureido, N,N,N′-trimethylureido), an alkylgroup (e.g., methyl, ethyl, propyl, butyl, pentyl, heptyl, octyl,isopropyl, s-butyl, t-amyl, cyclohexyl, cyclopentyl), an alkenyl group(e.g., vinyl, allyl, hexenyl), an alkynyl group (e.g., ethynyl,butynyl), an acyl group (e.g., formyl, acetyl, butyryl, hexanoyl,lauryl), an acyloxy group (e.g., acetoxy, butyryloxy, hexanoyloxy,lauryloxy), an alkoxy group (e.g., methoxy, ethoxy, propoxy, butoxy,pentyloxy, heptyloxy, oxtyloxy), an aryloxy group (e.g., phenoxy), analkoxycarbonyl group (e.g., methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, heptyloxycarbonyl),an aryloxycarbonyl group (e.g., phenoxycarbonyl), an alkoxycarbonylaminogroup (e.g., butoxycarbonylamino, hexyloxycarbonylamino), an alkylthiogroup (e.g., methylthio, ethylthio, propylthio, butylthio, pentylthio,heptylthio, octylthio), an arylthio group (e.g., phenylthio), analkylsulfonyl group (e.g., methylsulfonyl, ethylsulfonyl,propylsulfonyl, butylsulfonyl, pentylsulfonyl, heptylsulfonyl,octylsulfonyl), an amido group (e.g., acetamido, butylamido, hexylamido,laurylamido), and a non-aromatic heterocyclic group (e.g., morpholino,pyrazinyl).

Preferred substituent groups of the substituted aryl or substitutedaromatic heterocyclic group are a halogen atom, cyano, carboxyl,hydroxyl, amino, an alkyl-substituted amino group, an acyl group, anacyloxy group, an amido group, an alkoxycarbonyl group, an alkoxy group,an alkylthio group and an alkyl group.

The alkyl group and the alkyl moiety of the alkylamino group, thealkoxycarbonyl group or the alkoxy group may further have a substituentgroup. Examples of the substituent group of alkyl group or moietyinclude a halogen atom, hydroxyl, carboxyl, cyano, amino, an alkylaminogroup, nitro, sulfo, carbamoyl, an alkylcarbamoyl group, sulfamoyl, analkylsulfamoyl group, ureido, an alkylureido group, an alkenyl group, analkynyl group, an acyl group, an acyloxy group, an alkoxy group, anaryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, analkoxy-carbonylamino group, an alkylthio group, an arylthio group, analkylsulfonyl group, an amido group, and a non-aromatic heterocyclicgroup. Preferred substituent groups of alkyl group or moiety are ahalogen atom, hydroxyl, amino, an alkylamino group, an acyl group, anacyloxy group, an acylamino group, an alkoxycarbbnyl group, and analkoxy group.

In the formula (III), L¹ is a divalent linking group selected from thegroup consisting of an alkylene group, an alkenylene group, analkynylene group, a divalent saturated heterocyclic group, —O—, —CO— andcombinations thereof.

The alkylene group may have a cyclic structure. As the cyclic alkylenegroup, cyclohexylene is preferred and 1,4-cyclohexylene is particularlypreferred. If the alkylene group has a chain structure, a straight chainstructure is preferred to a branched one.

The alkylene group has preferably 1 to 20 carbon atoms, more preferably1 to 15 carbon atoms, further preferably 1 to 10 carbon atoms,furthermore preferably 1 to 8 carbon atoms, most preferably 1 to 6carbon atoms.

The alkenylene group or the alkynylene group preferably has a chainstructure, more preferably a straight chain structure.

The alkenylene group or the alkynylene group has preferably 2 to 10carbon atoms, more preferably 2 to 8 carbon atoms, further preferably 2to 6 carbon atoms, furthermore preferably 2 to 4 carbon atoms, mostpreferably 2 carbon atoms (namely, the alkenylene group or thealkynylene group is most preferably vinylene or ethynylene,respectively).

The divalent saturated heterocyclic group preferably has a 3- to9-membered heterocyclic ring. The hetero-atom in the heterocyclic groupis preferably oxygen, nitrogen, boron, sulfur, silicon, phosphorus orgermanium atom. Examples of the saturated heterocyclic ring includepiperidine ring, piperadine ring, morphorine ring, pyrrolidine ring,imidazoline ring, tetrahydrofuran ring, tetrahydropyran ring,1,3-dioxane ring, 1,4-dioxane ring, tetrahydrothiophene ring,1,3-thiazolidine ring, 1,3-oxazolidine ring, 1,3-dioxolan ring,1,3-dithiolan ring and 1,3,2-dioxaborane. Particularly preferreddivalent saturated heterocyclic groups are piperadine-1,4-diylene,1,3-dioxane-2,5-diylene and 1,3,2-dioxaborane-2,5-diylene.

Examples of the combined divalent linking group are shown below.

-   -   L-1: —O—CO-alkylene-CO—O—    -   L-2: —CO—O-alkylene-O—CO—    -   L-3: —O—CO-alkenylene-CO—O—    -   L-4: —CO—O-alkenylene-O—CO—    -   L-5: —O—CO-alkynylene-CO—O—    -   L-6: —CO—O-alkynylene-O—CO—    -   L-7: —O—CO-Ht-CO—O—    -   L-8: —CO—O-Ht-O—CO—        (Remark) —Ht: Divalent saturated heterocyclic group —In the        molecular structure represented by the formula (III), the angle        between Ar¹-L¹ and L¹-Ar² is 140° or more.

The rod-like compound is more preferably represented by the followingformula (IV):Ar¹-L²-X-L³-Ar².   (IV)

In the formula (IV), each of Ar¹ and Ar² is independently an aromaticgroup. The Ar¹ and Ar² are the same as those in the formula (III).

In the formula (IV), each of L² and L³ is independently a divalentlinking group selected from the group consisting of an alkylene group,—O—, —CO— and combinations thereof.

The alkylene group preferably has a chain structure, and a straightchain structure is preferred to a branched one.

The alkylene group has preferably 1,to 10 carbon atoms, more preferably1 to 8 carbon atoms, further preferably 1 to 6 carbon atoms, furthermorepreferably 1 to 4 carbon atoms, most preferably 1 to 2 carbon atoms(namely, the alkylene group is most preferably methylene or ethylene).

Each of L² and L³ is particularly preferably —O—CO— or —CO—O—.

In the formula (IV), X is 1,4-cyclohexylene, vinylene or ethynylene.

Examples of the compound represented by the formula (III) are asfollows.

Each of the above (1) to (34), (41), (42), (46), (47), (52) and (53) hastwo asymmetric carbons at the 1- and 4-positions of cyclohexane ring. Inspite of that, each compound of (1), (4) to (34), (41), (42), (46),(47), (52) and (53) has a symmetrical meso type-molecular structure, andhence has no optical (active) isomer but geometrical isomers (trans andcis-forms). The trans-form (1-trans) and cis-form (1-cis) of the abovecompound (1) are shown below.

The rod-like compound preferably has a linear molecular structure, asdescribed above. Accordingly, the transform is preferred to thecis-form.

Each of the above compounds (2) and (3) has not only geometrical isomersbut also optical isomers (four isomers in total). With respect to thegeometrical isomers, the trans-form is preferred to the cis-form.However, in view of the function, there is little difference between theoptical isomers, and hence either D- or L-body may be used. Further, itmay be racemate.

Each compound of (43) to (45) has trans- and cis-forms in connectionwith a vinylene bond at the central position. For the above-describedreason, the trans-form is preferred to the cis-form.

Two or more rod-like compounds (each of which gives the maximumabsorption peak at a wavelength (λmax) shorter than 250 nm in itsultraviolet absorption spectrum in the form of solution) may be used incombination.

The rod-like compound can be prepared according to the methods describedin, for example, Mol. Cryst. Liq. Cryst., 53(1979), pp. 229; ibid.,89(1982), pp. 93; ibid., 145(1987), pp. 111; ibid., 170(1989), pp. 43;J. Am. Chem. Soc., 113(1991), pp. 1349; ibid., 118(1996), pp. 5346;ibid., 92(19i0), pp. 1582; J. Org. Chem., 40(1975), pp. 420; andTetrahedron, 48(1992), No. 16, pp. 3437.

The retardation-increasing agent is incorporated in an amount ofpreferably 0.1 to 30 wt. %, more preferably 0.5 to 20 wt. %, based onthe amount of the polymer.

(Preparation of Polymer Film)

The polymer film is preferably prepared according to solvent castmethod. In the solvent cast method, a solution (dope) in which thepolymer is dissolved in an organic solvent is used.

Examples of the organic solvent include an ether having 2 to 12 carbonatoms, a ketone having 3 to 12 carbon atoms, an ester having 2 to 12carbon atoms, and a halogenated hydrocarbon having 1 to 6 carbon atoms.

The ether, the ketone or the ester may have a cyclic structure. Acompound having two or more functional groups of ether, ketone or ester(—O—, —CO— or —COO—) is also usable as the solvent. The organic solventmay have other functional groups such as alcoholic hydroxyl. If thesolvent is the compound having two or more functional groups, the numberof carbon atoms is in any of the above ranges.

Examples of the ether having 2 to 12 carbon atoms include dimethylether, diisopropyl ether, dimethoxymethane, dimethoxyethane,1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole.

Examples of the ketone having 3 to 12 carbon atoms include acetone,methylethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone andmethylcyclohexane.

Examples of the ester having 2 to 12 carbon atoms include methylformate, ethyl formate, propyl formate, pentyl formate, methyl acetate,ethyl acetate, and pentyl acetate.

Examples of the compound having two or more functional groups include2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

A typical example of the halogenated hydrocarbon having 1 to 6 carbonatoms is methylene chloride. From the technical viewpoint, thehalogenated hydrocarbon such as methylene chloride can be used withoutany problem. However, in consideration of the global environment andworking conditions, the organic solvent preferably contains essentiallyno halogenated hydrocarbon. This means the organic solvent preferablycontains halogenated hydrocarbon in an amount of less than 5 wt. % (morepreferably less than 2 wt. %). Also preferably, halogenated hydrocarbonsuch as methylene chloride is not found in the resultant film at all.

Two or more organic solvents may be mixed to use. In that case, alcoholor hydrocarbon can be used in addition to the above ether, ketone, esteror halogenated hydrocarbon.

The alcohol preferably has a boiling point of 30 to 170° C., and ispreferably a monohydric alcohol. The hydrocarbon moiety of the alcoholmay have a branched structure or a cyclic structure, and is preferably asaturated aliphatic hydrocarbon. The hydroxyl of the alcohol may beprimary, secondary or tertiary.

Examples of the alcohol include methanol (b.p.: 64.65° C.), ethanol(78.325° C.), 1-propanol (97.14° C.), 2-propanol (82.4° C.), 1-butanol(117.9° C.), 2-butanol (99.5° C.), t-butanol (82.45° C.), 1-pentanol(137.5° C.), 2-methyl-2-butanol (101.9° C.), cyclohexanol (161° C.),2-fluoroethanol (103° C.), 2,2,2-trifluoroethanol (80° C.),2,2,3,3-tetrafluoro-1-propanol (109° C.), 1,3-difluoro-2-propanol (55°C.), 1,1,1,3,3,3-hexa-2-methyl-2-propanol (62° C.),1,1,1,3,3,3-hexafluoro-2-propanol (59° C.),2,2,3,3,3-pentafluoro-1-propanol (80° C.),2,2,3,4,4,4-hexafluoro-1-butanol (114° C.),2,2,3,3,4,4,4-heptafluoro-1-butanol (97° C.), perfluoro-tert-butanol(45° C.), 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (142° C.),2,2,3,3,4,4-hexafluoro-1,5-pentanediol (111.5° C.),3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol (95° C.),2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoro-1-octanol (165° C.),1-(pentafluorophenyl)ethanol (82° C.) and 2,3,4,5,6-pentafluorobenzylalcohol (115° C.).

The hydrocarbon preferably has a boiling point of 30 to 170° C., and mayhave a branched structure or a cyclic structure. Either an aromatichydrocarbon or an aliphatic one can be used. The aliphatic hydrocarbonmay be unsaturated. Examples of the hydrocarbon include cyclohexane(b.p.: 80.7° C.), hexane (69° C.), benzene (80.° C.), toluene (110.1°C.) and xylene (138.4° C. to 144.4° C.).

When the polymer is dissolved in the solvent in a container, thecontainer may be filled with inert gas such as nitrogen gas. Theprepared polymer solution (dope) must be viscous enough to form a filmwhen cast on a support. The viscosity of the dope immediately beforecasting is normally in the range of 10 to 2,000 ps.s, preferably in therange of 30 to 400 ps.s.

The polymer solution (dope) can be prepared according to an ordinarymethod. The ordinary method means that the solution is prepared at atemperature of not lower than 0° C. (room temperature or elevatedtemperature). The polymer solution (dope) can be prepared through acommon process by means of a common apparatus in the normal solvent castmethod. In the normal process, a halogenated hydrocarbon (particularly,methylene chloride) is preferably used as the solvent.

The amount of the polymer in the solution is preferably in the range of10 to 40 wt. %, more preferably in the range of 10 to 30 wt. %. To theorganic (main) solvent, additives described below may be optionallyadded.

The polymer and the organic solvent are mixed and stirred at roomtemperature (0 to 40° C.) to prepare the solution. For preparing theconcentrated solution, the preparation may be carried out at an elevatedtemperature under a high pressure. In that case, the polymer and theorganic solvent are placed in a vessel resisting pressure. After thevessel is sealed, the mixture is stirred under an increased pressure atan elevated temperature. The temperature is controlled so that it may behigher than the boiling point of the solvent at atmospheric pressure butso that the solvent may not boil. The temperature is normally in therange of 40° C. or more, preferably in the range of 60 to 200° C., morepreferably in the range of 80 to 110° C.

The components can be preliminary dispersed coarsely, and the coarsedispersion can be placed in the vessel. Otherwise, the components canalso be introduced into the vessel in series. The vessel should beequipped with a stirring device. A pressure in the vessel can be formedby introducing an inert gas such as nitrogen gas into the vessel, or byheating and evaporating the solvent to increase the vapor pressure.Further, the components can be added to the vessel at a high pressureafter the vessel is sealed.

The vessel is preferably heated from outside. For example, a jacketheater is preferably used. Otherwise, liquid heated with a plate-heaterplaced outside of the vessel may be circulated through a pipe woundaround the vessel, to heat the whole vessel.

The mixture is preferably stirred with a propeller mixer provided in thevessel. The wing of the propeller preferably has a length reaching theinside wall of the vessel. Further, at the tip of-the wing, a scratchingmean is provided to scratch and renew liquid attached on the insidewall.

In the vessel, various meters such as pressure gauge and thermometer maybe provided. After the components are dissolved in the solvent in thevessel, the prepared dope may be cooled and then taken out of thevessel, or may be taken out and then cooled with a heat exchanger.

The solution can be prepared according to the cooling dissolutionmethod, which makes it possible to dissolve the polymer in an organicsolvent in which the polymer cannot be dissolved by a conventionalprocess. Further, according to the method, the polymer can be rapidlyand homogeneously dissolved in an organic solvent in which the polymercan be dissolved by a conventional process.

First in the process of cooling dissolution method, the polymer isgradually added with stirring into an organic solvent at roomtemperature. The amount of the polymer in the mixture is preferably inthe range of 10 to 40 wt. %, more preferably in the range of 10 to 30wt. %. Various additives described below may be added in the mixture.

The prepared mixture is cooled to a temperature of −100 to −10° C.,preferably −80 to −10° C., more preferably −50 to −20° C., mostpreferably −50 to −30° C. The cooling procedure can be carried out, forexample, with dry ice-methanol bath (−75° C.) or with cooled ethyleneglycol solution (−30 to −20° C.). Through the cooling procedure, themixture is solidified.

The cooling rate is preferably 4° C./minute or more, more preferably 8°C./minute or more, and most preferably 12° C./minute or more. Thecooling rate is preferably as fast as possible. However, a theoreticalupper limit of the cooling rate is 10,000° C./second, a technical upperlimit is 1,000° C./second, and a practical upper limit is 100°C./second. The cooling rate means the change of temperature at thecooling step per the time taken to complete the cooling step. The changeof temperature means the difference between the temperature at which thecooling step is started and the temperature at which the cooling step iscompleted.

The cooled mixture is then warmed to a temperature of 0 to 200° C.,preferably 0 to 150° C., more preferably 0 to 120° C., most preferably 0to 50° C. Through the warming procedure, the polymer is dissolved in theorganic solvent. For warming, the mixture may be left at roomtemperature or may be heated in a warm bath.

The warming rate is 4° C./minute or more, more preferably 8° C./minuteor more, and most preferably 12° C./minute or more. The warming rate ispreferably as fast as possible. However, a theoretical upper limit ofthe cooling rate is 10,000° C./second, a technical upper limit is 1,000°C./second, and a practical upper limit is 100° C./second. The warmingrate means the change of temperature at the warming step per the timetaken to complete the warming step. The change of temperature means thedifference between the temperature at which the warming step is startedand the temperature at which the warming step is completed.

Thus, a homogeneous solution can be prepared. If the polymer is notsufficiently dissolved, the cooling and warming procedures may berepeated. It can be judged by observation with the eyes whether thepolymer is sufficiently dissolved or not.

In the process of cooling dissolution method, a sealed vessel ispreferably used to prevent contamination of water, which may be causedby dew condensation at the cooling step. Further, the mixture may becooled under a reduced pressure so that the time taken to complete thecooling step can be shortened, and hence a vessel resisting pressure ispreferably used to conduct the procedures under a reduced pressure.

According to differential scanning calorimetric measurement (DSC), a 20wt. % solution prepared by dissolving cellulose acetate (acetic acidcontent: 60.9%, viscosity average polymerization degree: 299) in methylacetate through the cooling dissolution process has a pseudo-phasetransition point between gel and sol at approx. 33° C. Below thattemperature, the solution is in the form of homogeneous gel. Thesolution, therefore, must be kept at a temperature above thepseudo-phase transition point, preferably at a temperature higher thanthe pseudo-phase transition point by approx. 10° C. The pseudo-phasetransition point depends upon various conditions such as the organicsolvent, the acetic acid content, the viscosity average polymerizationdegree and the concentration of cellulose acetate.

The polymer film is formed from the prepared polymer solution (dope)according to the solvent cast method.

The dope is cast on a drum or a band, and the solvent is evaporated toform a film. The solid content of the dope is preferably controlled inthe range of 18 to 35%. The surface of the drum or band is preferablybeforehand polished to be a mirror. The casting and drying steps of thesolvent cast method are described in U.S. Pat. Nos. 2,336,310,2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069,2,739,070, British Patent Nos. 640,731, 736,892, Japanese PatentPublication Nos. 45(1970)-4554, 49(1974)-5614, Japanese PatentProvisional Publication Nos. 60(1985)-176834, 60(1985)-203430 and62(1987)-115035.

The surface temperature of the drum or band is preferably 10° C. orbelow. After cast on the drum or band, the dope is blown with air for 2seconds or more to dry. The formed film is then peeled, and blown withhot air whose temperature is successively changed from 100° C. to 160°C. in order to evaporate remaining solvent. This procedure is describedin Japanese Patent Publication No. 5(1993)-17844. The procedure canshorten the time taken to complete the steps of cooling to peeling. Forperforming the procedure, the cast dope must gel at the surfacetemperature of the drum or band.

Two or more polymer solutions (dopes) may be prepared, and from them twoor more layers may be formed by the solvent cast method to prepare alayered polymer film. The dopes are cast on a drum or a band, and thesolvent is evaporated to form the film. The solid content of each dopeis preferably controlled in the range of 10 to 40%. The surface of thedrum or band is preferably beforehand polished to be a mirror.

In the case where two or more polymer solutions are cooperatively cast,two or more outlets are arranged at intervals along the runningdirection of the support (drum or band), and from each outlet eachpolymer solution is cast to form a layered film (Japanese PatentProvisional Publication Nos. 61(1986)-158414, 1(1989)-122419 and11(1999)-198285). Otherwise, polymer solutions may be cast from twooutlets to form a film (Japanese Patent Publication No. 60(1985)-27562,Japanese Patent Provisional Publication Nos. 61(1986)-94724,61(1986)-947245, 61(1986)-104813, 61(1986)-158413 and 6(1994)-134933).Further, a flow of high-viscous polymer solution may be enclosed with aflow of low-viscous one to form a layered flow, and the high- andlow-viscous solutions in the layered flow may be simultaneously extrudedto produce a film (Japanese Patent Provisional Publication No.56(1981)-162617).

Further, the method disclosed in Japanese Patent Publication No.44(1969)-20235 may be adopted. In the disclosed process, a polymersolution is cast on the support from one outlet to form a film. Afterpeeled from the support, the formed film is turned over and again placedon the support. On the thus appearing surface (having been in contactwith the support), another polymer solution is cast from another outletto form a film.

The used polymer solutions may be the same or different from each other.The function of each formed polymer layer can be given by eachcorresponding solution extruded from each outlet.

Other functional layers (e.g., adhesive layer, dye layer, antistaticlayer, anti-halation layer, UV absorbing layer, polarizing layer) can besimultaneously formed together with the polymer layer in the abovemanner.

In a conventional single layer preparation process, it is necessary toextrude a polymer solution having such high concentration and such highviscosity that the resultant film may have the aimed thickness.Accordingly, that polymer solution is often so unstable that solidcontents are deposited to cause troubles and to impair the planeness. Toavoid the problem, plural concentrated polymer solutions aresimultaneously extruded from outlets onto the support. The thus-preparedthick film has excellent planeness. In addition, since the concentratedsolutions are used, the film is so easily dried that the productivity(particularly, production speed) can be improved.

A plasticizer can be added into the polymer solution to enhancemechanical strength of the resultant film or to shorten the time fordrying. The plasticizer is, for example, a phosphate ester or acarbonate ester. Examples of the phosphate ester used as the plasticizerinclude triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Typicalexamples of the carbonate ester are phthalate esters and citrate esters.Examples of the phthalate esters include dimethyl phthalate (DMP),diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate(DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP).Examples of the citrate esters include triethyl o-acetylcitrate (OACTE)and tributyl o-acetylcitrate (OACTB). Besides the above, butyl oleate,methylacetyl ricinolate, dibutyl sebacate and various trimellitic estersare also usable. The plasticizers of phosphate esters (DMP, DEP, DBP,DOP, DPP, DEHP) are preferred. Particularly preferred are DEP and DPP.

The content of the plasticizer is preferably in the range of 0.1 to 25wt. %, more preferably in the range of 1 to 20 wt. %, most preferably inthe range of 3 to 15 wt. % based on the amount of the polymer.

Further, a deterioration inhibitor (e.g., oxidation inhibitor, peroxidedecomposer, radical inhibitor, metal inactivating agent, oxygenscavenger, amine) may be incorporated in the polymer film. Thedeterioration inhibitor is described in Japanese-Patent ProvisionalPublication Nos. 3(1991)-199201, 5(1993)-1907073, 5(1993)-194789,5(1993)-271471 and 6(1994)-107854. The content of the deteriorationinhibitor is preferably in the range of 0.01 to 1 wt. %, more preferablyin the range of 0.01 to 0.2 wt. % based on the amount of the dope. Ifthe content is less than 0.01 wt. %, the deterioration inhibitor giveslittle effect. If the content is more than 1 wt. %, the inhibitor oftenoozes out (bleeds out) to appear on the surface of the film.Particularly preferred deterioration inhibitors are butylatedhydroxytoluene (BHT) and tribenzylamine (TBA).

In order to make the film easily treatable during the productionprocess, a matting layer containing a matting agent and a polymer may beprovided. As the matting agent and the polymer, materials described inJapanese Patent Provisional Publication No. 10(1998)-44327 arepreferably used.

The polymer film has a thickness preferably in the range of 10 to 200μm, more preferably in the range of 20 to 150 μm, most preferably in therange of 30 to 140 μm.

The birefringence of the film measured at the wavelength of 550 nm ispreferably in the range of 0.00196 to 0.01375, more preferably in therange of 0.00168 to 0.006875, most preferably in the range of 0.00275 to0.00458.

(Stretching of Film)

The retardation of the polymer film can be controlled by stretching.

The stretching ratio (the ratio of length increased by stretching basedon the original length) is preferably in the range of 3 to 100%, morepreferably in the range of 5 to 80%, most preferably in the range of 10to 60%. The film may be stretched either uniaxially or biaxially.

In the biaxial stretching, the film is simultaneously or successively(step-by-step) stretched in two directions (namely, simultaneous biaxialstretching or successive biaxial stretching). The successive biaxialstretching is preferred in consideration of continuous production. Theprocess of the successive biaxial stretching comprises the steps ofcasting the dope onto a band or a drum, peeling the formed film,stretching the film laterally (perpendicularly to the castingdirection), and then stretching the film longitudinally. Thelongitudinal stretching step may be performed prior to the lateralstretching.

Japanese Patent Provisional Publication Nos. 62(1987)-115035,4(1992)-152125, 4(1992)-284211, 4(1992)-298310 and 11(1999)-48271describe the lateral stretching, which is performed at room temperatureor an elevated temperature. The elevated temperature is preferably belowthe glass transition point of the film. The film can be stretched whilebeing dried in the film production. If the film is stretched while thesolvent still remains in the film, a special effect is sometimesobtained. The longitudinal stretching can be performed, for example, bycontrolling the conveying rollers so that the speed of winding up thefilm may be faster than that of peeling the film. The lateralstretching, on the other hand, can be performed by gradually wideningthe width between tenters clipping both sides of the conveyed film.Otherwise, after the film is dried, it can be stretched by means of astretching machine (preferably, the film is uniaxially stretched bymeans of a long stretching machine).

The steps from casting to drying may be performed under inert atmosphere(e.g., nitrogen gas atmosphere). For winding up the film, generally usedmachines can be used. Examples of the winding method include a constanttension method, a constant torque method, a taper tension method and aprogrammed tension control method by which inner stress is keptconstant.

(Surface Treatment of Polymer Film)

The polymer film is preferably subjected to surface treatment. Examplesof the surface treatment include corona discharge treatment, glowdischarge treatment, flame treatment, acid treatment, alkali treatment,and ultraviolet (UV) treatment. Further, in place of or in addition tothe surface treatment, an undercoating layer (described in JapanesePatent Provisional Publication No. 7(1995)-333433) may be provided.

For ensuring the planeness of the film, the above treatments are carriedout preferably at a temperature not higher than Tg (glass transitiontemperature) of the film. That is not higher than 150° C.

In the case where the film is used as a protective film of thepolarizing plate, the acid or alkali treatment is preferably carried outin consideration of adhesion between the film and the plate. If the filmis made of cellulose ester, the surface of the film is saponified by theacid or alkali treatment.

It is particularly preferred to subject the polymer film to the alkalitreatment for saponifying.

As the alkali treatment, the steps of immersing the film surface in analkaline solution, neutralizing with an acidic solution, washing withwater, and drying are preferably circularly carried out.

Examples of the alkaline solution include aqueous solutions of KOH andNaOH. The normality of hydroxyl ion is preferably in the range of 0.1 to3.0 N,.more preferably in the range of 0.5 to 2.0 N. The temperature ofthe solution is preferably in the range of room temperature to 90° C.,more preferably in the range of 40 to 70° C.

In the saponification process, the-alkaline solution may be applied onthe film surface in place of immersing. As the solvent for the coatingsolution, organic solvent or a mixture of organic solvent and water ispreferred. Examples of the organic solvent include alcohols (e.g.,methanol, ethanol, butanol, isopropyl alcohol), ketones (e.g., acetone,methyl ethyl ketone) and polyhydric alcohols (e.g., propylene glycol,ethylene glycol). Two or more organic solvents may be mixed to used incombination.

The surface energy of the film subjected to the surface treatment ispreferably not less than 55 mN/m, more preferably in the range of 60 to75 mN/m.

The surface energy can be measured by the contact angle method, the wetheating method or the adsorption method (these methods are described in‘The basic theory and application of wetting (written in Japanese)’,published by Realize Co., Ltd, 1989). The contact angle method ispreferred. In that method, two solutions having known surface energiesare dropped onto the film. The contact angle of each drop is measured,and the surface energy of the film is calculated from the measuredcontact angles. The contact angle is, by definition, an angle (includingthe drop) between the film surface and the tangent of the drop surfaceat the crossing point.

(Orientation Layer)

The polymer film by itself can be used as an optical compensatory sheet.

Otherwise, the polymer film may be used as a support on which anoptically anisotropic layer formed from liquid crystal compound isprovided. In that case, an orientation layer for aligning the liquidcrystal molecules is preferably provided between the polymer film andthe anisotropic layer.

If once the alignment of the liquid crystal molecules is fixed afterthey are oriented, the orientation layer has already accomplished itswork and hence the resultant compensatory sheet does not need tocomprise the orientation layer. In fact, the optically anisotropic layercontaining the aligned and fixed liquid crystal molecules can be alonetransferred (without the orientation layer) onto the polymer film, toprepare an optical compensatory sheet.

An orientation layer has a function for aligning the liquid crystalmolecules.

The orientation layer can be formed by rubbing treatment of an organiccompound (preferably a polymer), oblique evaporation of an inorganiccompound, formation of a micro groove layer, or stimulation of anorganic compound (e.g., ω-tricosanoic acid, dioctadecylmethylammoniumchloride, methyl stearate) according to a Langmuir-Blodgett method.Further, the aligning function of the orientation layer can be activatedby applying an electric or magnetic field to the layer or irradiatingthe layer with light.

The orientation layer is preferably formed by rubbing a polymer. As thepolymer for orientation layer, two or more polymer materials may be usedin combination.

For ensuring durability of the optical compensatory sheet, the polymerfor orientation layer is preferably crosslinked at any stage from thestep of applying the orientation layer on the polymer film to the stepof producing the resultant compensatory sheet.

Preferably, two or more polymers are crosslinked and subjected to therubbing treatment to form the orientation layer. In that case, at leastone polymer is preferably crosslinkable by itself or with a crosslinkingagent.

Polymers having functional groups can be reacted with light, heat or pHvariation to form a crosslinked structure. Otherwise, linking groups areintroduced by a reactive crosslinking agent into the polymers so thatthe polymers can be crosslinked to form the crosslinked structure.

In a normal process, a coating liquid containing the polymers and, ifneeded, the crosslinking agent is applied on the polymer film, and then,for example, heated to induce the crosslinking reaction. The coatingliquid is preferably heated to such a relatively low temperature at thisstage that the orientation layer is fully crosslinked in a subsequentheating treatment for forming the optically anisotropic layer describedbelow.

In consideration of orientation of liquid crystal moleculars in theoptically anisotropic layer on the orientation layer, the polymer fororientation layer is preferably fully crosslinked after the moleculesare aligned.

Examples of the polymer for orientation layer include polymethylmethacrylate, polyacrylic acid, polymethacrylic acid, polystyrene,polymaleinimide, polyvinyl alcohol, denatured polyvinyl alcohol,poly(N-methylolacrylamide), gelatin, polyvinyl toluene, chlorosulfonatedpolyethylene, cellulose nitrate, polyvinyl chloride, chlorinatedpoly-olefin, polyester, polyimide, polyvinyl acetate, carboxymethylcellulose, polyethylene, polypropylene, and polycarbonate. Theorientation layer may be also prepared from a coupling agent (e.g.,silan coupling agent).

A copolymer comprising two or more repeating units is also usable.Examples of the copolymers include acrylic acid/methacrylic acidcopolymer, styrene/maleinimide copolymer, styrene/vinyltoluenecopolymer, vinyl acetate/vinyl chloride copolymer, and ethylene/vinylacetate copolymer.

Preferred examples are water-soluble polymers such aspoly(N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinylalcohol and denatured polyvinyl alcohol. Gelatin, polyvinyl alcohol anddenatured polyvinyl alcohol are particularly preferred, and polyvinylalcohol and denatured polyvinyl alcohol are further preferred. Adenatured polyvinyl alcohol having hydrophobic group is particularlypreferred.

It is most preferred to use two kinds of polyvinyl alcohols or denaturedpolyvinyl alcohols having different polymerization degrees.

The saponification degree of the polyvinyl alcohol or the denaturedpolyvinyl alcohol is in the range of 70 to 100%, preferably in the rangeof 80 to 100%, more preferably in the range of 85 to 95%. Thepolymerization degree is preferably in the range of 100 to 3,000.Examples of the denatured polyvinyl alcohol include polyvinyl alcoholsdenatured by copolymerization, by chain transfer and by blockpolymerization. Examples of the denaturing group in the copolymerizationinclude COONa, —Si(OR)₃ in which R is hydrogen or an alkyl group,—N(CH₃)₃.Cl, —C₉H₁₉, —COOR, —SO₃Na and —C₁₂H₂₅. Examples of thedenaturing group in the chain transfer include COONa, SH and C₁₂H₂₅.Examples of the denaturing group in the block polymerization include—COOH, —CONH₂, —COOR (R is hydrogen or an alkyl group) and —C₆H₅.

The compound represented by the following formula (V) is particularlypreferably used as a denaturing agent of polyvinyl alcohol.

In the formula (V), R¹ is an alkyl group, an acryloylalkyl group, amethacryloylalkyl group, an acryloyloxyalkyl group, amethacryloyloxyalkyl group or an epoxyalkyl group; W is a halogen atom,an alkyl group or an alkoxy group; X is an atomic group required to forman active ester, an acid anhydride or a acid halide; p is 0 or 1; and nis an integer of 0 to 4.

The denatured polyvinyl alcohol is more preferably a product of reactionbetween polyvinyl alcohol and the compound represented by the followingformula (VI):

in which X¹ is an atomic group required to form an active ester, an acidanhydride or a acid halide; and m is an integer of 2 to 24.

The denaturing agent represented by the above formula (V) may be reactedwith not only non-denatured polyvinyl alcohol but also polyvinylalcohols denatured by copolymerization, by chain transfer or by blockpolymerization. Preferred examples of the denatured polyvinyl alcoholare described in Japanese Patent Provisional Publication No.9(1997)-152509.

With respect to the denatured polyvinyl alcohol, Japanese PatentProvisional Publication No. 8(1996)-338913 describes the synthesis, themeasurement of visible absorption spectrum and how to determine theamount of introduced denaturing groups.

Examples of the crosslinking agent include aldehydes, (e.g.,formaldehyde, glyoxal, glutaraldehyde), N-methylol compounds (e.g.,dimethylol urea, methyloldimethyl-hydantoin), dioxane derivatives (e.g.,2,3-dihydroxydioxane), compounds that works when the carboxylic group isactivated (e.g., carbenium, 2-naphthalenesulfonate,1,1-bispyrrolidino-1-chloropyridinium,1-morpholinocarbonyl-3-(sulfonatoaminomethyl), active vinyl compounds(e.g., 1,3,5-triacryloyl-hexahydro-s-triazine, bis(vinylsulfone)methane,N,N′-methylenebis[β-(vinylsulfonyl)propionamide), active halogencompounds (e.g., 2,4-dichloro-6-hydroxy-s-triazine), isooxazoles anddialdehyde starch. Two or more crosslinking agents may be used incombination.

They are effectively used together with preferably water-solublepolymer, more preferably polyvinyl alcohol or denatured polyvinylalcohol. Reactive aldehydes are preferred, and glutaraldehyde isparticularly preferred in consideration of productivity.

The more the crosslinking agent is added, the more the durabilityagainst moisture is improved. However, if the amount of crosslinkingagent is too much, the resultant orientation layer poorly aligns themolecules. Accordingly, the amount of crosslinking agent is preferablyin the range of 0.1 to 20 wt. %, more preferably in the range of 0.5 to15 wt. % based on the amount of the polymer.

Even after the crosslinking reaction is completed, the obtainedorientation layer contains non-reacted crosslinking agent a little. Theamount of the non-reacted crosslinking agent remaining in theorientation layer is preferably not more than 1.0 wt. %, more preferablynot more than 0.5 wt. % based on the amount of the orientation layer. Ifthe layer contains the non-reacted agent in an amount of more than 1.0wt. %, the layer has poor durability. A liquid crystal displaycomprising such orientation layer often suffers troubles of reticulationif used for a long time or left under hot and humid condition.

The orientation layer can be formed by the steps of coating the polymerfilm with a coating liquid containing the above polymer and (if needed)the crosslinking agent, heating to dry and crosslink the appliedpolymer, and subjecting the formed layer to rubbing treatment. Thecrosslinking reaction may be caused at any step after applying thecoating liquid.

In the case where a water-soluble polymer such as polyvinyl alcohol isused, the coating solution is preferably prepared from a mixed solventof water and an organic solvent having defoaming character (e.g.,methanol). The content of methanol in the mixed solvent is preferably 1wt. % or more, more preferably 9 wt. % or more. Because of defoamingcharacter of the organic solvent, defects on the orientation layer areremarkably decreased, and accordingly the optically anisotropic layerhas an improved surface.

As the coating method, known methods such as spin-coating, dip-coating,curtain-coating, extrusion-coating, bar-coating and E type-coating canbe adopted. The E type-coating method is particularly preferred.

The thickness of the orientation layer is preferably in the range of 0.1to 10 μm. The layer of applied coating solution is preferably dried at atemperature of 20 to 110° C. For ensuring sufficient crosslinking, thetemperature is more preferably in the range of 60 to 100° C., mostpreferably in the range of 80 to 100° C. The time for drying ispreferably in the range of 1 minute to 36 hours, more preferably in therange of 5 minute to 30 minutes. The pH is also preferably adjusted atan optimal value according to the used crosslinking agent. Ifglutaraldehyde is used as the crosslinking agent, the pH is preferablyin the range of 4.5 to 5.5, more preferably at 5.0.

The rubbing treatment can be conducted in the manner adopted widely foraligning liquid crystal molecules of liquid crystal display. The surfaceof the layer is rubbed with paper, cloth (gauze, felt, nylon, polyester)or rubber along a certain direction, to give the aligning function.Generally, the layer is rubbed several times with cloth on which fibershaving the same length and thickness are provided.

(Optically Anisotropic Layer)

The optically anisotropic layer prepared from a liquid crystal compoundis provided on the orientation layer.

The liquid crystal compound composing the optically anisotropic layermay be a rod-like liquid crystal compound or a discotic one. Therod-like or discotic liquid crystal compound may have a low molecularweight or a high molecular weight. Further, even if a low molecularweight liquid crystal compound is crosslinked to become a compound thatdoes not behave as liquid crystal, that compound is also usable.

For preparing the optically anisotropic layer, a solution containing theliquid crystal compound and other optional components (such aspolymerization initiator) is applied on the orientation layer.

A solvent for preparing the solution is preferably an organic solvent.Examples of the organic solvents include amides (e.g.,N,N-dimethylformamide), sulfoxides (e.g., di-methylsulfoxide),heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene,hexane), alkyl halides (e.g., chloroform, dichloromethane,tetrachloroethane), esters (e.g., methyl acetate, butyl acetate),ketones (e.g., acetone, methyl ethyl ketone) and ethers (e.g.,tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones arepreferred. Two or more organic solvents can be used in combination.

The solution can be coated according to a conventional coating methodsuch as a wire-bar coating method, an extrusion coating method, a directgravure coating method, a reverse gravure coating method or a diecoating method.

The thickness of the optically anisotropic layer is preferably in therange of 0.1 to 20 μm, more preferably in the range of 0.5 to 15 μm,most preferably in the range of 1 to 10 μm.

Examples of the rod-like liquid crystal compound include azomethines,azoxys, cyanobiphenyls, cyanophenyl esters, benzoic esters,cyclohexanecarboxylate phenyl esters, cyanophenylcyclohexanes,cyano-substituted phenylpyrimidines, alkoxy-substitutedphenylpyrimidines, phenyldioxanes, tolanes, andalkenylcyclohexylbenzonitriles.

Metal complexes are also included in the rod-like liquid crystalcompounds. Further, a liquid crystal polymer in which the repeating unitcomprises a rod-like liquid crystal moiety is also usable as therod-like liquid crystal compound. In other words, the rod-like liquidcrystal compound may be combined with a (liquid crystal) polymer.

Descriptions of the rod-like liquid crystal compounds are found in“Kagaku-Sosetsu, Ekisho no Kageku” (written in Japanese), vol. 22(1994),Chapters 4, 7 and 11; and “Ekisho Devise Handbook” (written inJapanese), chapter 3.

The rod-like liquid crystal compound preferably has a birefringencialindex of 0.001 to 0.7.

The molecule of the rod-like liquid crystal compound preferably has apolymerizable group (Q) to fix the alignment.

Examples of the polymerizable group (Q) are shown below.

The polymerizable group (Q) preferably is an unsaturated polymerizablegroup (Q1 to Q7) or an epoxy group (Q8), more preferably is anunsaturated polymerizable group; and most preferably is an ethylenicallyunsaturated group (Q1 to Q6).

However, as the liquid crystal compound used in the invention, adiscotic liquid crystal compound is preferred to a rod-like one.

Examples of the discotic liquid crystal compound include benzenederivatives described in C. Destrade et al., Mol. Cryst. vol. 71, pp.111, (1981); truxene derivatives described in C. Destrade et al., MolCryst. vol. 122, pp. 141. (1985), Physics lett. A, vol. 78, pp. 82,(1990); cyclohexane derivatives described in B. Kohn et al., Angew.

Chem. vol. 96, pp. 70, (1984); and macrocyclic compounds ofazacrown-type or phenylacetylene-type described in J. M. Lehn et al., J.Chem. Commun. pp. 1794, (1985), and J. Zhang et al., J. Am. Chem. Soc.vol. 116, pp.2655, (1994).

The discotic compound has a structure in which the discotic structureunit is located at the center as a parent core and further straightchain groups such as alkyl, alkoxy and substituted benzoyloxy areradially substituted. The discotic compound generally has the propertiesof liquid crystal. However, it is not necessary for the resultant layerto contain the discotic compound in the above-described form. Forexample, the low molecular weight discotic liquid crystal compoundhaving a thermo- or photo-reactive group is polymerized by heat or lightto form a polymer that does not behave as liquid crystal. Such polymercan be also used in the invention.

Preferred examples of the discotic liquid crystal compound are describedin Japanese Patent Provisional Publication No. 8(1996)-50206. JapanesePatent Provisional Publication No. 8(1996)-27284 describespolymerization of the discotic liquid crystal compound.

For fixing the discotic liquid crystal molecules, a polymerizable groupshould be bound to a discotic core of the molecule to cause thepolymerization reaction. However, if the polymerizable group is directlybound to the discotic core, it is difficult to keep the alignment at thepolymerization reaction. Therefore, a linking group is introducedbetween the discotic core and the polymerizable group. Accordingly, thediscotic compound having a polymerizable group preferably is a compoundrepresented by the following formula (III).D(-L-O)_(n)   (VII)in which D is a discotic core; L is a divalent linking group; Q is apolymerizable group; and n is an integer of 4 to 12.

Examples of the discotic cores (D) are shown below. In the examples, LQ(or QL) means the combination of the divalent linking group (L) and thepolymerizable group (Q).

In the formula (VII), the divalent linking group (L) is preferablyselected from the group consisting of an alkylene group, an alkenylenegroup, an arylene group, —CO—, —NH—, —O—, —S— and combinations thereof.The L is more preferably a divalent linking group comprising at leasttwo divalent groups selected from the group consisting of an alkylenegroup, an arylene group, —CO—, —NH—, —O— and —S—. The L more preferablyis a divalent linking group comprising at least two divalent groupsselected from the group consisting of an alkylene group, an arylenegroup, —CO— and —O—. The alkylene group preferably has 1 to 12 carbonatoms. The alkenylene group preferably has 2 to 12 carbon atoms. Thearylene group preferably has 6 to 10 carbon atoms.

Examples of the divalent linking groups (L) are shown below. In theexamples, the left side is attached to the discotic core (D), and theright side is attached to the polymerizable group (Q). The AL means analkylene group or an alkenylene group. The AR means an arylene group.The alkylene group, the alkenylene group and the arylene group may havea substituent group (e.g., an alkyl group).

-   -   L1: —AL—CO—O—AL—    -   L2: —AL—CO—O—AL—O—    -   L3: —AL—CO—O—AL—O—AL—    -   L4: —AL—CO—O—AL—O—CO—    -   L5: —CO—AR—O—AL—    -   L6: —CO—AR—O—AL—O—    -   L7: —CO—AR—O—AL—O—CO—    -   L8: —CO—NH—AL—    -   L9: —NH—AL—O—    -   L10: —NH—AL—O—CO—    -   L11: —O—AL—    -   L12: —O—AL—O—    -   L13: —O—AL—O—CO—    -   L14: —O—AL—O—CO—NH—AL—    -   L15: —O—AL—S—AL—    -   L16: —O—CO—AR—O—AL—CO—    -   L17: —O—CO—AR—O—AL—O—CO—    -   L18: —O—CO—AR—O—AL—O—AL—O—CO—    -   L19: —O—CO—AR—O—AL—O—AL—O—AL—O—CO—    -   L20: —S—AL—    -   L21: —S—AL—O—    -   L22: —S—AL—O—CO—    -   L23: —S—AL—S—AL—    -   L24: —S—AR—AL—

The definition and examples of the polymerizable groups (Q) in theformula (VII) are the same as those shown above for rod-like liquidcrystal compound.

The polymerizable group (Q) preferably is an unsaturated polymerizablegroup (Q1 to Q7) or an epoxy group (Q8), more preferably is anunsaturated polymerizable group, and most preferably is an ethylenicallyunsaturated group (Q1 to Q6).

In the formula (VII), n is an integer of 4 to 12, which is determinedaccording to the structure of the discotic core (D). The 4 to 12combinations of L and Q may be different from each other. However, thecombinations are preferably identical.

If the discotic compound is used, the discotic structure unit of eachdiscotic molecule preferably has a plane inclined from the plane of thepolymer film at an angle varying in the direction of depth of the layer.

The above-described angle (inclined angle) of the plane of discoticstructure unit generally increases or decreases with increase ofdistance in the direction of depth from the bottom of the opticallyanisotropic layer. The inclined angle preferably increases with increaseof the distance. Further, examples of variation of the inclined angleinclude continuous increase,” continuous decrease, intermittentincrease, intermittent decrease, variation containing continuousincrease and decrease, and intermittent variation containing increase ordecrease. The intermittent variation contains an area where the inclinedangle does not vary in the course of the thickness direction of thelayer. The inclined angle preferably totally increases or decreases inthe layer, even if it does not vary in the course. The inclined anglemore preferably increases totally, and it is particularly preferred toincrease continuously.

The inclined angle of the discotic unit near the support can begenerally controlled by selecting the discotic compound or materials ofthe orientation layer, or by selecting methods for the rubbingtreatment. The inclined angle of the discotic unit near the surface(air) can be generally controlled by selecting the discotic compound orother compounds used together with the discotic compound. Examples ofthe compounds used together with the discotic compound includeplasticizer, surface active agent, polymerizable monomer and polymer.Further, the extent of variation of the inclined angle can be alsocontrolled by the above selection. A polymerizable monomer or polymer ispreferably used.

It is particularly preferred to use polymerizable monomers (e.g.,compounds having a vinyl, vinyloxy, acryloyl or methacryloyl group)together with the discotic liquid crystal compound. Those monomers arepreferably used in the amount of 1 to 50 wt. % (especially 5 to 30 wt.%) based on the amount of the discotic compound. The adhesion betweenthe orientation layer and the optically anisotropic layer can beenhanced with a polymerizable monomer having four or more reactivefunctional groups.

The polymer is preferably cellulose derivatives. Examples of thecellulose derivatives include cellulose acetate, cellulose acetatepropionate, hydrocypropyl cellulose, and cellulose acetate butylate. Theamount of the polymer is preferably in the range of 0.1 to 10 wt. % ,more preferably in the range of 0.1 to 8 wt. %, most preferably in therange of 0.1 to 5 wt. % based on the amount of the discotic liquidcrystal compound.

In the case where the optically anisotropic layer is prepared from thediscotic liquid crystal compound, it can be generally prepared by thesteps of: coating the orientation layer with a solution of the discoticcompound and other compounds dissolved in a solvent, drying, heating toa temperature for forming a discotic nematic phase, and cooling with theoriented condition (discotic nematic phase) kept. Otherwise, the layercan be prepared by the steps of: coating the orientation layer with asolution of the discotic compound and other compounds (e.g.,polymerizable monomer, photo-polymerization initiator) dissolved in asolvent, drying, heating to a temperature for forming a discotic nematicphase, polymerizing the heated layer (e.g., by radiation of UV light)and cooling. The transition temperature from discotic nematic phase tosolid phase is preferably in the range of 70 to 300° C., especially 70to 170° C.

The aligned liquid crystal molecules can be fixed with the alignmentmaintained. The liquid crystal molecules are fixed preferably by apolymerization reaction. The polymerization reaction can be classifiedinto a thermal reaction with a thermal polymerization initiator and aphotoreaction with a photo polymerization initiator. A photopolymerization reaction is preferred.

Examples of the photo polymerization initiators include α-carbonylcompounds (described in U.S. Pat. Nos. 2,367,661, 2,367,670), acyloinethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon substitutedacyloin compounds (described in U.S. Pat. No. 2,722,512), polycyclicquinone compounds (described in U.S. Pat. Nos. 2,951,758, 3,046,127),combinations of triarylimidazoles and p-aminophenyl ketones (describedin U.S. Pat. No. 3,549,367), acridine or phenazine compounds (describedin Japanese Patent Provisional Publication No. 60(1985)-105667 and U.S.Pat. No. 4,239,850) and oxadiazole compounds (described in U.S. Pat. No.4,212,970).

The amount of the photo polymerization initiator is preferably in therange of 0.01 to 20 wt. %, and more preferably in the range of 0.5 to 5wt. % based on the solid content of the coating solution.

The light irradiation for the photo polymerization is preferablyconducted with ultraviolet rays.

The exposure energy is preferably in the range of 20 to 50,000 mJ/cm²,more preferably in the range of 20 to 5,000 mJ/cm², most preferably inthe range of 100to 800 mJ/cm². The light irradiation can be conductedwhile the layer is heated to accelerate the photo polymerizationreaction.

The protective layer may be provided on the optically anisotropic layer.

(Polarizing Plate)

The polarizing plate comprises two transparent protective films and apolarizing membrane provided between the films. One of the protectivefilms may be the optical compensatory sheet of the invention, and theother may be a normal cellulose acetate film.

Examples of the polarizing membrane include an iodine polarizingmembrane, a polyene polarizing membrane and a dichromatic dye polarizingmembrane. The iodine polarizing membrane and the dye polarizing membraneare generally prepared from polyvinyl alcohol films.

It has been found that the moisture-permeability of the protective filmis important for production of the polarizing plate. In producing thepolarizing plate, the polarizing membrane and the protective film arelaminated with an aqueous adhesive, and then the solvent of the adhesiveis diffused into the film to dry. The higher permeability the film has,the more rapidly it is dried. Accordingly, the productivity of thepolarizing plate is improved. However, if the permeability is too high,moisture in air is liable to come into the membrane to impairpolarizability if the liquid crystal display is used under humidcondition.

(Liquid Crystal Display)

The optical compensatory sheet of the invention or a polarizing platecomprising the sheet of the invention laminated on a polarizing membraneis advantageously used in an image-displaying device, particularly in aliquid crystal display, especially in a liquid crystal display oftransmission type.

A liquid crystal display of transmission type comprises a pair ofpolarizing plates and a liquid crystal cell placed between them. Thepolarizing plate comprises a pair of transparent protective films and apolarizing membrane placed between them. The liquid crystal cellcomprises a pair of electrode substrates and liquid crystal providedbetween them.

The optical compensatory sheet of the invention is placed between thecell and one or each of the polarizing plates.

The liquid crystal cell works preferably according to VA mode, OCB mode,IPS mode or TN mode.

In a liquid crystal cell of VA mode, rod-like liquid crystal moleculesare essentially vertically aligned while voltage is not applied.

The liquid crystal cell of VA mode include some types: (1) a liquidcrystal cell of VA mode in a narrow sense (described in Japanese PatentProvisional Publication No. 2(1990)-176625), in which rod-like liquidcrystal molecules are essentially vertically aligned while voltage isnot applied, and the molecules are essentially horizontally alignedwhile voltage is applied; (2) a liquid crystal cell of MVA mode(described in SID97, Digest of tech. Papers, 28(1997), 845), in whichthe VA mode is modified to be multi-domain type so as to enlarge theviewing angle; (3) a liquid crystal cell of n-ASM mode (described inAbstracts of Japanese Forum of Liquid Crystal (written in Japanese),(1998), pp. 58 to 59), in which rod-like liquid crystal molecules areessentially vertically aligned while voltage is not applied, and themolecules are essentially oriented in twisted multi-domain alignmentwhile voltage is applied; and (4) a cell of SURVAIVAL mode (presented inLCD International '98).

The liquid crystal cell of OCB mode is a liquid crystal cell of bendalignment mode in which rod-like liquid crystal molecules in upper partand ones in lower part are essentially reversely (symmetrically)aligned. A liquid crystal display having the liquid crystal cell of bendalignment mode is disclosed in U.S. Pat. Nos. 4,583,825 and 5,410,422.Since rod-like liquid crystal molecules in upper part and ones in lowerpart are symmetrically aligned, the liquid crystal cell of bendalignment mode has self-optical compensatory function. Therefore, thismode is referred to as OCB (optically compensatory bend) mode. Theliquid crystal display of bend alignment mode has an advantage ofresponding rapidly.

In a liquid crystal cell of TN mode, rod-like liquid crystal moleculesare essentially horizontally aligned while voltage is not applied, andoriented in a twisted alignment with a twisted angle of 60 to 120°. Theliquid crystal cell of TN mode is widely used in color TFT liquidcrystal displays, and hence is described in many publications.

When an image-displaying device displays a dark image, the chromaticityor transmittance of image often fluctuates in response to the viewingangle. The optical compensatory sheet of the invention prevents thefluctuation of chromaticity or transmittance.

The fluctuations of chromaticity and transmittance can be evaluated inthe following manner. In the below-described examples, they are alsoevaluated in the following manners.

(Viewing Angle Dependence of Chromaticity)

The chromaticity of image is preferably represented in Luv coordinate,in order to visually express fluctuation. A sensory fluctuation inchromaticity can be evaluated in terms of Cuv value defined by thefollowing formulas:Cuv=(u* ² +v* ²)^(1/2)u*=u−u ₀v*=v−v ₀

The chromaticity fluctuation Cuv is preferably 0.07 or less, morepreferably 0.05 or less, further preferably 0.04 or less, and mostpreferably 0.03 or less. If the Cuv is 0.07 or less, there ispractically no problem. If the Cuv is 0.03 or less, the chromaticityfluctuation cannot be recognized with the naked eyes.

(Viewing Angle Dependence of Transmittance)

The fluctuation of transmittance ΔT(60) is defined by the followingformula:ΔT(60)={T(60)−T(0)}/T(0)×100in which

T(60): a transmittance observed in the direction in plane at 45° upperfrom the absorption axis of polarizing plate on the observer side and at40° inclined from the front when a dark image is displayed, and

T(0): a transmittance frontally observed when a dark image is displayed.

The ΔT(60) is preferably 10% or less, more preferably 5% or less,further preferably 3% or less, and most preferably 2% or less. If theΔT(60) is 10% or less, there is practically no problem. If the ΔT(60) is2% or less, the fluctuation of transmittance cannot be recognized withthe naked eyes.

[Preliminary Experiment]

The absorption spectra of retardation-increasing agents (10-trans,41-trans and 29-trans) were measured in the ultraviolet-visiblewavelength region.

Each agent was dissolved in tetrahydrofuran without stabilizer (BHT), toprepare a 10⁻⁵ mol/dm³ solution. The absorption spectrum of the preparedsolution was measured by means of a spectrometer (HITACHI, LTD). Theresults are set forth in Table 1. TABLE 1

Retardation Absorption coefficient increasing Maximum wave- (ε) atmaximum absorp- agent length (λmax) tion 10-trans 220 nm 15,000 41-trans230 nm 16,000 29-trans 240 nm 20,000

EXAMPLE 1

(Preparation of Polymer Film)

At room temperature, 100 weight parts of cellulose acetate (averageacetic acid content: 60.3%), 7.8 weight parts of triphenyl phosphate,3.9 weight parts of biphenyldiphenyl phosphate, 1.32 weight parts of theretardation-increasing agent (41-trans), 587.69 weight parts ofmethylene chloride, and 50.85 weight parts of methanol were mixed toprepare a solution (dope).

The prepared dope was cast on a band, dried at room temperature for 1minute, and further dried at 45° C. for 5 minutes, so that the amount ofremaining solvent was 30 wt. %. After peeled from the band, the formedfilm was laterally stretched by 25% at 140° C. by means of a tenter. Thestretched film was then dried at 135° C. for 20 minutes. The amount ofthe solvent remaining in the obtained film was 0.1 wt. %.

The thickness of the film was 98 μm. The Re retardation values of thefilm were measured at the wavelength of 450 nm, 550 nm and 590 nm bymeans of an ellipsometer (M-150, JEOL COORPORATION), and found 31 nm, 34nm and 35 nm, respectively. The Rth values were also measured at thewavelength of 450 nm, 550 nm and 590 nm, and found 120 nm, 132 nm and135 nm, respectively.

The thus-prepared polymer film was used as an optical compensatorysheet.

(Preparation of Polarizing Plate)

Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare apolarizing membrane. On one surface of the membrane, the opticalcompensatory sheet was laminated with polyvinyl adhesive. The membraneand the sheet were positioned so that the transmission axis of themembrane might be parallel to the slow axis of the sheet.

A commercially available triacetyl cellulose film (Fujitac TD80, FujiPhoto Film Co., Ltd.) was saponified, and laminated on the other surfaceof the polarizing membrane with polyvinyl adhesive. Thus, a polarizingplate was prepared.

(Preparation of Liquid Crystal Display)

A pair of polarizing plates and a pair of phaseretarders were removedfrom a commercially available liquid crystal display (VL-1530S, Fujitsu,Ltd.), which had a liquid crystal cell comprising vertically alignedliquid crystal molecules. In place of the removed members, the preparedpolarizing plates were laminated so that the optical compensatory sheetsmight be on the liquid crystal cell side. The polarizing plate on theobserver side was placed so that the transmission axis might be in theup-down direction, while the plate on the backlight side was placed sothat the transmission axis might be in the left-right direction. Thus,the polarizing plates were arranged in cross-Nicol position.

The viewing angle of the prepared liquid crystal display was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 2.

COMPARISON EXAMPLE 1

The viewing angle of the commercially available liquid crystal display(VL-1530S, Fujitsu, Ltd.), which had a liquid crystal cell comprisingvertically aligned liquid crystal molecules, was measured by means of ameasuring apparatus (EZ-Contrast 160D, ELDIM) when each of eight tonesof black (L1) to white (L8) was displayed. The results are set forth inTable 2. TABLE 2 Viewing angle giving contrast ratio of 10 or morewithout reversing gray scale between L1 and L2 along transmission at 45°to transmission Liquid crystal display axis axis Example 1 >80° >80°Comparison Example 1 >80°  44°

EXAMPLE 2

(Preparation of Polymer Film)

At room temperature, 100 weight parts of cellulose acetate (averageacetic acid content: 60.9%), 4.6 weight parts of theretardation-increasing agent (10-trans), 7.8 weight parts of triphenylphosphate, 3.9 weight parts of biphenyldiphenyl phosphate, 594.61 weightparts of methylene chloride and 52.14 weight parts of methanol weremixed to prepare a solution (dope).

The prepared dope was cast on a band, dried at room temperature for 1minute, and further dried at 45° C. for 5 minutes, so that the amount ofremaining solvent was 30 wt. %. After peeled from the band, the formedfilm was laterally stretched by 28% at 140° C. by means of a tenter. Thestretched film was then dried at 135° C. for 20 minutes. The amount ofthe solvent remaining in the obtained film was 0.1 wt. %. The thicknessof the film was 92 μm. The Re retardation values of the film weremeasured at the wavelength of 450 nm, 550 nm and 590 nm by means of anellipsometer (M-150, JEOL COORPORATION), and found 39 nm, 42 nm and 43nm, respectively. The Rth values were also measured at the wavelength of450 nm, 550.nm and 590 nm, and found 158 nm, 172 nm and 175 nm,respectively.

The thus-prepared polymer film was used as a support of opticalcompensatory sheet.

(Preparation of Optical Compensatory Sheet)

The polymer film was immersed in a 2.0 N aqueous KOH solution for 2minutes (25° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-saponified film wasmeasured according to the contact angle method, to find 63 mN/m.

On the saponified surface, the following coating solution was thenapplied in the amount of 28 ml/m² by means of a wire bar coater of #16.The applied solution was dried with hot air at 60° C. for 60 seconds,and then further dried with hot air at 90° C. for 150 seconds.

The formed layer was subjected to the rubbing treatment in which therubbing direction was at the angle of 45° to the slow axis (measured at632.8 nm) of the polymer film, to form an orientation layer. Coatingsolution for orientation layer The following denatured polyvinyl alcohol10 weight parts Water 371 weight parts Methanol 119 weight partsGlutaric aldehyde (crosslinking agent) 0.5 weight part Denaturedpolyvinyl alcohol

To prepare another coating solution, 41.01 g of the following discoticliquid crystal compound, 4.06 g of ethylene oxide denaturedtrimethlolpropanetriacrylate (V#360, Osaka Organic Chemicals Co., Ltd.),0.35 g of cellulose acetate butyrate (CAB-531-1, Eastman Chemical), 1.35g of a photopolymerization initiator (Irgacure 907, Ciba-Geigy) and 0.45g of a sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) weredissolved in 102 g of methyl ethyl ketone. The coating solution was thenapplied on the orientation layer by means of a wire bar coater of #3.The thus-treated film was fixed on a metal frame, and maintained in athermostat at 130° C. for 2 minutes to align the molecules of thediscotic compound. The film was then irradiated at 130° C. for 1 minutewith ultraviolet rays emitted from a high-pressure mercury lamp of 120W/cm, to polymerize the discotic compound. The film was cooled to roomtemperature. Thus, an optical compensatory sheet was formed.Discotic Liquid Crystal Compound

The Re retardation value was measured at 546 nm, and found 38, nm. Theaverage angle (inclined angle) between the disc plane and the polymerfilm was 40°.

(Preparation of Polarizing Plate)

Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare apolarizing membrane. On one surface of the membrane, the opticalcompensatory sheet was laminated with polyvinyl adhesive. The membraneand the sheet were positioned so that the transmission axis of themembrane might be parallel to the slow axis of the sheet.

A commercially available triacetyl cellulose film (Fujitac TD80, FujiPhoto Film Co., Ltd.) was saponified, and laminated on the other surfaceof the polarizing membrane with polyvinyl adhesive. The membrane and thefilm were positioned so that the transmission axis of the membrane mightbe perpendicular to the slow axis of the film. Thus, a polarizing platewas prepared.

(Preparation of Liquid Crystal Display)

On a glass plate having an ITO electrode, an orientation film ofpolyimide was provided and subjected to a rubbing treatment. Thisprocedure was repeated to prepare two substrates, and the substrateswere arranged face-to-face so that the rubbing directions might beparallel and that the cell gap might be 6 μm. Between them, a liquidcrystal having Δn of 0.1396 (ZLI1132, Merck & Co., Inc.) was introducedto prepare a liquid crystal cell of bend alignment.

Two polarizing plates prepared above were laminated on the liquidcrystal cell so that the cell might be between the plates. The plateswere arranged so that the optically anisotropic layer in each platemight face to the cell substrate and that the rubbing directions of thecell and the optically anisotropic layer might be anti-parallel.

Voltage of a square wave (55 Hz) was applied to the liquid crystal cell.An image was displayed according to normally white mode (white: 2V,black: 5V). A ratio of the transmittance (white/black) was measured as acontrast ratio by means of a meter (EZ-Contrast 160D, ELDIM) at eightdisplaying states of L1 (full black) to L8 (full white). From theobtained contrast ratio, the viewing angle of the prepared liquidcrystal display was measured. The results are set forth in Table 3.TABLE 3 Liquid Viewing angle giving contrast ratio of 10 or more crystalwithout reversing gray scale between L1 and L2 display Upward DownwardLeftward-rightward Ex. 2 80° 80° 80°

EXAMPLE 3

(Preparation of Polymer Film)

At room temperature, 100 weight parts of cellulose acetate (averageacetic acid content: 59.5%), 4.00 weight parts of theretardation-increasing agent (41-trans), 7.8 weight parts of triphenylphosphate, 3.9 weight parts of biphenyldiphenyl phosphate, 594.02 weightparts of methylene chloride and 51.49 weight parts of methanol weremixed to prepare a solution (dope).

The prepared dope was cast on a band, dried at room temperature for 1minute, and further dried at 45° C. for 5 minutes, so that the amount ofremaining solvent was 30 wt. %. After peeled from the band, the formedfilm was laterally stretched by 35% at 140° C. by means of a tenter. Thestretched film was then dried at 135° C. for 20 minutes. The amount ofthe solvent remaining in the obtained film was 0.1 wt. %.

The thickness of the film was 119.5 μm. The Re retardation values of thefilm were measured at the wavelength of 450 nm, 550 nm and 590 nm bymeans of an ellipsometer (M-150, JEOL COORPORATION), and found 42 nm, 46nm and 47 nm, respectively. The Rth values were also measured at thewavelength of 450 nm, 550 nm and 590 nm, and found 133 nm, 145 nm and148 nm, respectively.

The thus-prepared polymer film was used as an optical compensatorysheet.

(Preparation of Polarizing Plate)

Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare apolarizing membrane. On one surface of the membrane, the opticalcompensatory sheet was laminated with polyvinyl adhesive. The membraneand the sheet were positioned so that the transmission axis of themembrane might be parallel to the slow axis of the sheet.

A commercially available triacetyl cellulose film (Fujitac TD80, FujiPhoto Film Co., Ltd.) was saponified, and laminated on the other surfaceof the polarizing membrane with polyvinyl adhesive. Thus, a polarizingplate was prepared.

(Preparation of Liquid Crystal Display)

A pair of polarizing plates was removed from a commercially availableliquid crystal display (6E-A3, Sharp Corporation), which had a liquidcrystal cell of TN mode. In place of the removed members, the polarizingplate prepared above was laminated on each side (each of the backlightside and the observer side) of the cell with an adhesive so that theoptical compensatory sheet might be on the liquid crystal cell side. Thepolarizing plates were arranged so that their transmission axes might bein O-mode position.

The viewing angle of the prepared liquid crystal display was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 4.

COMPARISON EXAMPLE 2

The viewing angle of the commercially available liquid crystal display(6E-A3, Sharp Corporation), which had a liquid crystal cell of TN mode,was measured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of eight tones of black (L1) to white (L8) was displayed. Theresults are set forth in Table 4. TABLE 4 Viewing angle giving contrastratio of 10 or more without reversing gray Liquid crystal scale betweenL1 and L2 display Upward Downward Leftward-rightward Example 3 18° 23°77° Comparison Example 2 15° 25° 37°

EXAMPLE 4

(Preparation of Polymer Film)

At room temperature, 20 weight parts of cellulose triacetate (averageacetic acid content: 60.3%, viscosity average polymerization degree:320, water content: 0.4 wt. %, viscosity of 6 wt. % methylene chloridesolution: 305 mpa-s, in the form of powder in which the means particlesize is 1.5 mm and the standard deviation is 0.5 mm), 58 weight parts ofmethyl acetate, 5 weight parts of acetone, 5 weight parts of methanol, 5weight parts of ethanol, 5 weight parts of butanol, 1.2 weight parts ofditrimethylol-propane tetracetate (plasticizer), 1.2 weight parts oftriphenyl phosphate (plasticizer), 0.2 weight part of2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine(UV absorber), 0.2 weight part of2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorbenzotriazole (UVabsorber), 0.2 weight part of2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)-5-chlorbenzotriazole (UVabsorber), 0.02 weight part of C₁₂H₂₅OCH₂CH₂O—P(═O)−(OK)₂ (releasingagent), 0.02 weight part of citric acid (releasing agent) and 0.05weight part of silica particles (particle size: 20 nm, Mohs hardnessnumber: approx. 7) were mixed to prepare a solution (dope).

The used cellulose triacetate contained 0.01 wt. % or less of theremaining acetic acid, 0.05 wt. % of Ca, 0.007 wt. % of Mg, and 5 ppm ofFe. The substitution degree at 6-position was 0.95, which was 32.2%based on the total substitution degree at 2-, 3- and 6-positions. Theextract with acetone was 11 wt. %. The ratio between weight and numberaverage molecular weights was 0.5, and evenly distributed. Theyellowness index, the haze, the transmittance, the glass transitiontemperature (Tg) and the heat of crystallization were 0.3, 0.08, 93.5%,160° C. and 6.2 J/g, respectively.

In another mixing tank, 2.25 weight parts of the retardation-increasingagent (41-trans), 16.0 weight parts of methylene chloride and 1.39weight parts of methanol were placed, heated and stirred, to prepare aretardation-increasing agent solution.

The cellulose acetate solution and the retardation-increasing agentsolution were mixed and stirred well to prepare a dope

The dope was cast and dried. The amount of solvent remaining in theformed film was 0.5%.

The thickness of the film was 65 μm. The Re retardation values of thefilm were measured at the wavelength of 450 nm, 550 nm and 590 nm bymeans of an ellipsometer (M-150, JEOL COORPORATION), and found 7.2 nm,7.8 nm and 8 nm, respectively. The Rth values were also measured at thewavelength of 450 nm, 550 nm and 590 nm, and found 70 nm, 76 nm and 78nm, respectively.

The thus-prepared polymer film was used as a support of opticalcompensatory sheet.

(Preparation of Optical Compensatory Sheet)

The polymer film was immersed in a 2.0 N aqueous KOH solution for 2minutes (25° C.), neutralized with sulfuric acid, washed with purewater, and dried. The surface energy of the thus-saponified film wasmeasured according to the contact angle method, to find 63 mN/m.

On the saponified surface, the following coating solution was thenapplied in the amount of 28 ml/m² by means of a wire bar coater of #16.The applied solution was dried with hot air at 60° C. for 60 seconds,and then further dried with hot air at 90° C. for 150 seconds.

The formed layer was subjected to the rubbing treatment in which therubbing direction was parallel to the longitudinal direction of thepolymer film, to form an orientation layer. Coating solution fororientation layer The denatured polyvinyl alcohol used in Example 2   10weight parts Water  371 weight parts Methanol  119 weight parts Glutaricaldehyde (crosslinking agent)  0.5 weight part

To prepare another coating solution, 41.01 g of the discotic liquidcrystal compound used in Example 2, 4.06 g of ethylene oxide denaturedtrimethlolpropanetriacrylate (V#360, Osaka Organic Chemicals Co., Ltd.),0.90 g of cellulose acetate butyrate (CAB-531-0.2, Eastman Chemical),0.23 g of cellulose acetate butyrate (CAB-531-1, Eastman Chemical), 1.35g of a photopolymerization initiator (Irgacure 907, Ciba-Geigy) and 0.45g of a sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) weredissolved in 102 g of methyl ethyl ketone. The coating solution was thenapplied on the orientation layer by means of a wire bar coater of #3.6.The thus-treated film was heated at 130° C. for 2 minutes to align themolecules of the discotic compound. The film was then irradiated at 60°C. for 1 minute with ultraviolet rays emitted from a high-pressuremercury lamp of 120 W/cm, to polymerize the discotic compound. The filmwas cooled to room temperature, to form an optically anisotropic layer.Thus, an optical compensatory sheet was formed.

The Re retardation value was measured at 546 nm, and found 43 nm. Theaverage angle (inclined angle) between the disc plane and the celluloseacetate film was 42°.

(Preparation of Polarizing Plate)

Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare apolarizing membrane. On one surface of the membrane, the opticalcompensatory sheet was laminated with polyvinyl adhesive. The membraneand the sheet were positioned so that the transmission axis of themembrane might be parallel to the slow axis of the sheet.

A commercially available triacetyl cellulose film (Fujitac TD80, FujiPhoto Film Co., Ltd.) was saponified, and laminated on the other surfaceof the polarizing membrane with polyvinyl adhesive. The membrane and thefilm were positioned so that the transmission axis of the membrane mightbe perpendicular to the slow axis of the film. Thus, a polarizing platewas prepared.

(Preparation of Liquid Crystal Display)

A pair of polarizing plates was removed from a commercially availableliquid crystal display (AQUOS LC-20C1-S, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, thepolarizing plate prepared above was laminated on each side (each of thebacklight side and the observer side) of the cell with an adhesive sothat the optical compensatory sheet might be on the liquid crystal cellside. The polarizing plates were arranged so that their transmissionaxes might be perpendicular to each other.

The viewing angle of the prepared liquid crystal display was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 5.

COMPARISON EXAMPLE 3

A pair of polarizing plates was removed from a commercially availableliquid crystal display (AQUOS LC-20C1-S, Sharp Corporation), which had aliquid crystal cell of TN mode. In place of the removed members, acommercially available polarizing plate was laminated on each side (eachof the backlight side and the observer side) of the cell with anadhesive so that the optical compensatory sheet might be on the liquidcrystal cell side. The polarizing plates were arranged so that theirtransmission axes might be perpendicular to each other.

The viewing angle of the prepared liquid crystal display was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results areset forth in Table 5. TABLE 5 Viewing angle giving contrast ratio of 10or more without reversing gray Liquid crystal scale between L1 and L2display Upward Downward Leftward-rightward Example 4 80° 45° 160°Comparison Example 3 15° 25°  37°

COMPARISON EXAMPLE 4

(Preparation of Polymer Film)

A polycarbonate film (thickness: 60 μm) was 1.23 times stretched at 167°C. by means of a tenter.

The Re retardation values of the film were measured at the wavelength of450 nm, 550 nm and 590 nm by means of an ellipsometer (M-150, JEOLCOORPORATION), and found 128 nm, 120 nm and 114 nm, respectively. TheRth values were also measured at the wavelength of 450 nm, 550 nm and590 nm, and found 214 nm, 200 nm and 190 nm, respectively.

The thus-prepared polymer film was used as an optical compensatorysheet.

(Preparation of Polarizing Plate)

Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare apolarizing membrane. On one surface of the membrane, the opticalcompensatory sheet was laminated with polyvinyl adhesive. The membraneand the sheet were positioned so that the transmission axis of themembrane might be parallel to the slow axis of the sheet.

A commercially available triacetyl cellulose film (Fujitac TD80, FujiPhoto Film Co., Ltd.) was saponified, and laminated on the other surfaceof the polarizing membrane with polyvinyl adhesive. The membrane and thefilm were positioned so that the transmission axis of the membrane mightbe perpendicular to the slow axis of the film. Thus, a polarizing platewas prepared.

(Preparation of Liquid Crystal Display)

A pair of polarizing plates was removed from a commercially availableliquid crystal display (6E-A3, Sharp Corporation), which had a liquidcrystal cell of TN mode. In place of the removed members, the polarizingplate prepared above was laminated on each side (each of the backlightside and the observer side) of the cell with an adhesive so that theoptical compensatory sheet might be on the liquid crystal cell side. Thepolarizing plates were arranged so that their transmission axes might bein O-mode position.

The viewing angle of the prepared liquid crystal display was measured bymeans of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each ofeight tones of black (L1) to white (L8) was displayed. The results werealmost the same as those in example 3, but it was noted that thedisplayed dark image was colored red when obliquely seen.

EXAMPLE 5

(Preparation of Liquid Crystal Display)

On a glass substrate having an ITO transparent electrode, a polymer forforming a vertical orientation layer (LQ-1800, Hitachi-Du PontMicrosystems Co., Ltd.) was applied, dried and subjected to rubbingtreatment. This procedure was repeated to obtain two glass substrateswith orientation layer.

The prepared two substrates were face-to-face placed so that theorientation layers might face to each other and so that the rubbingdirection of the orientation layers might be anti-parallel, and a spacerof 7.6 μm was inserted between the substrates. The substrates were thenlaminated. To the gap between the substrates, a liquid crystal compound(ZLI-2806, Merck) was injected according to the vacuum injection method,to form a liquid crystal layer. Thus, a cell of bend alignment mode wasprepared.

On each surface of the cell, the polarizing plate prepared in Example 3was laminated. The plates were placed so that the transmission axis ofeach plate might be at 45° to the rubbing direction of the cell.

Voltage of a square wave 1 kHz was applied, and a ratio of thetransmittance (white/black) was measured as a contrast ratio by means ofa meter (EZ-Contrast 160D, ELDIM) at eight displaying states of L1 (fullblack) to L8 (full white). From the obtained contrast ratio, the viewingangle of the prepared liquid crystal display was measured. The resultsare set forth in Table 6. TABLE 6 Liquid Viewing angle giving contrastratio of 10 or more crystal without reversing gray scale between L1 andL2 display Upward Downward Leftward-rightward Ex. 5 65° 40° 100°(Fluctuations of Chromaticity and Transmittance in Response to ViewingAngle)

With respect to the liquid crystal displays prepared in Examples 1 to 4and Comparison Example 1, fluctuations of chromaticity and transmittancein response to the viewing angle were evaluated in the aforementionedmanners. The results are set forth in Table 7. TABLE 7 Liquid crystaldisplay Mode Cuv ΔT(60) Example 1 MVA 0.045 2.7% Example 2 OCB 0.0331.8% Example 3 TN 0.067 8.5% Example 4 TN 0.055 4.5% Comparison Example4 TN 0.150 20.5%

As shown in Table 7, the invention of each mode satisfyingly reduces thefluctuations of chromaticity and transmittance, as compared with thecomparison example.

1. An optical compensatory sheet which consists of a polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm.
 2. The optical compensatory sheetof claim 1, wherein the polymer film has an Re retardation value ofRe450 measured at the wavelength of 450 nm in the range of 10 to 60 nm,and an Re retardation value of Re590 measured at the wavelength of 590nm in the range of 20 to 70 nm, said values of Re450 and Re590satisfying the condition of Re590-Re450≧2 nm.
 3. The opticalcompensatory sheet of claim 1, wherein the polymer film is made ofcellulose ester.
 4. The optical compensatory sheet of claim 1, whereinthe polymer film is a film stretched with a stretching ratio of 3 to100%.
 5. The optical compensatory sheet of claim 1, wherein the rod-likecompound has a linear molecular structure.
 6. The optical compensatorysheet of claim 1, wherein the rod-like compound is liquid crystal. 7.The optical compensatory sheet of claim 1, wherein the rod-like compoundis represented by the formula (III):Ar¹-L¹-Ar²   (III) in which each of Ar¹ and Ar² independently is anaromatic group; and L¹ is a divalent linking group selected from thegroup consisting of an alkylene group, an alkenylene group, analkynylene group, a divalent saturated heterocyclic group, —O—, —CO— anda combination thereof.
 8. The optical compensatory sheet of claim 7,wherein the rod-like compound is represented by the formula (IV):Ar¹-L²-X-L³-Ar²   (IV) in which each of Ar¹ and Ar² independently is anaromatic group; each of L² and L³ independently is a divalent linkinggroup selected from the group consisting of an alkylene group, —O—, —CO—and a combination thereof; and X is 1,4-cyclohexylene, vinylene orethynylene.
 9. An image display device having an optical compensatorysheet, wherein the optical compensatory sheet consists of a polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm.
 10. A polarizing plate comprising apair of transparent protective films and a polarizing membrane providedbetween the transparent protective films, wherein at least one of theprotective films is an optical compensatory sheet which consists of apolymer film containing a rod-like compound, which gives an ultravioletabsorption spectrum, in which the wavelength of λmax at the maximumabsorption peak is shorter than 250 nm, said spectrum of the rod-likecompound being measured when the rod-like compound is in the form of asolution, wherein the polymer film has an Rth retardation value ofRth450 measured at the wavelength of 450 nm in the range of 30 to 160nm, and an Rth retardation value of Rth590 measured at the wavelength of590 nm in the range of 50 to 200 nm, said values of the Rth450 andRth590 satisfying the condition of Rth590-Rth450≧2 nm, and wherein theoptical compensatory sheet and the polarizing membrane are so placedthat the transmission axis of the membrane is parallel or perpendicularto the slow axis of the polymer film.
 11. An image display device havinga polarizing plate, said polarizing plate comprising a pair oftransparent protective films and a polarizing membrane provided betweenthe transparent protective films, wherein at least one of the protectivefilms is an optical compensatory sheet which consists of a polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm, and wherein the opticalcompensatory sheet and the polarizing membrane are so placed that thetransmission axis of the membrane is parallel or perpendicular to theslow axis of the polymer film.
 12. An optical compensatory sheet whichcomprises an optically anisotropic layer and a polymer film, saidoptically anisotropic layer being formed from a liquid crystal compound,and said polymer film containing a rod-like compound, which gives anultraviolet absorption spectrum, in which the wavelength of λmax at themaximum absorption peak is shorter than 250 nm, said spectrum of therod-like compound being measured when the rod-like compound is in theform of a solution, wherein the polymer film has an Rth retardationvalue of Rth450 measured at the wavelength of 450 nm in the range of 30to 160 nm, and an Rth retardation value of Rth590 measured at thewavelength of 590 nm in the range of 50 to 200 nm, said values of theRth450 and Rth590 satisfying the condition of Rth590-Rth450≧2 nm. 13.The optical compensatory sheet of claim 12, wherein the polymer film hasan Re retardation value of Re450 measured at the wavelength of 450 nm inthe range of 10 to 60 nm, and an Re retardation value of Re590 measuredat the wavelength of 590 nm in the range of 20 to 70 nm, said values ofRe450 and Re590 satisfying the condition of Re590-Re450≧2 nm.
 14. Theoptical compensatory sheet of claim 12, wherein the polymer film is madeof cellulose ester.
 15. The optical compensatory sheet of claim 12,wherein the polymer film is a film stretched with a stretching ratio of3 to 100%.
 16. The optical compensatory sheet of claim 12, wherein therod-like compound has a linear molecular structure.
 17. The opticalcompensatory sheet of claim 12, wherein the rod-like compound is liquidcrystal.
 18. The optical compensatory sheet of claim 12, wherein therod-like compound is represented by the formula (III):Ar¹-L¹-Ar²   (III) in which each of Ar¹ and Ar² independently is anaromatic group; and L¹ is a divalent linking group selected from thegroup consisting of an alkylene group, an alkenylene group, analkynylene group, a divalent saturated heterocyclic group, —O—, —CO— anda combination thereof.
 19. The optical compensatory sheet of claim 18,wherein the rod-like compound is represented by the formula (IV):Ar¹-L²-X-L³-Ar²   (IV) in which each of Ar¹ and Ar² independently is anaromatic group; each of L² and L³ independently is a divalent linkinggroup selected from the group consisting of an alkylene group, —O—, —CO—and a combination thereof; and X is 1,4-cyclohexylene, vinylene orethynylene.
 20. An image display device having an optical compensatorysheet, wherein the optical compensatory sheet comprises an opticallyanisotropic layer and a polymer film, said optically anisotropic layerbeing formed from a liquid crystal compound, and said polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm.
 21. A polarizing plate comprising apair of transparent protective films and a polarizing membrane providedbetween the transparent protective films, wherein at least one of theprotective films is an optical compensatory sheet which comprises anoptically anisotropic layer and a polymer film, said opticallyanisotropic layer being formed from a liquid crystal compound, and saidpolymer film containing a rod-like compound, which gives an ultravioletabsorption spectrum, in which the wavelength of λmax at the maximumabsorption peak is shorter than 250 nm, said spectrum of the rod-likecompound being measured when the rod-like compound is in the form of asolution, wherein the polymer film has an Rth retardation value ofRth450 measured at the wavelength of 450 nm in the range of 30 to 160nm, and an Rth retardation value of Rth590 measured at the wavelength of590 nm in the range of 50 to 200 nm, said values of the Rth450 andRth590 satisfying the condition of Rth590-Rth450≧2 nm, and wherein theoptical compensatory sheet and the polarizing membrane are so placedthat the transmission axis of the membrane is parallel or perpendicularto the slow axis of the polymer film.
 22. An image display device havinga polarizing plate, said polarizing plate comprising a pair oftransparent protective films and a polarizing membrane provided betweenthe transparent protective films, wherein at least one of the protectivefilms is an optical compensatory sheet which comprises an opticallyanisotropic layer and a polymer film, said optically anisotropic layerbeing formed from a liquid crystal compound, and said polymer filmcontaining a rod-like compound, which gives an ultraviolet absorptionspectrum, in which the wavelength of λmax at the maximum absorption peakis shorter than 250 nm, said spectrum of the rod-like compound beingmeasured when the rod-like compound is in the form of a solution,wherein the polymer film has an Rth retardation value of Rth450 measuredat the wavelength of 450 nm in the range of 30 to 160 nm, and an Rthretardation value of Rth590 measured at the wavelength of 590 nm in therange of 50 to 200 nm, said values of the Rth450 and Rth590 satisfyingthe condition of Rth590-Rth450≧2 nm, and wherein the opticalcompensatory sheet and the polarizing membrane are so placed that thetransmission axis of the membrane is parallel or perpendicular to theslow axis of the polymer film.